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Scuba compressor in campervan, which invertor ? battery ? ...help


Hi everyone, please help ...

We are a van conversion company. One of our next customers is a scuba diver and will be off grid with I suppose 370W solar panel. His Sprinter 2019 doesn't have a smart alternator. He wants to have a compressor in his van to fill the Oxygen tank. He wants Victron material with about 300W solar panel and a relay charger. He will have a hook up possibility but won't have regular access. Traveling in Africa and Scotland ... extreme temperature.


the compressor that would run for about 30min every 2-3 days.


I emailed the company to have more info regarding the starting power, here tare the different answers I received.


“The start up current for the MCH6, 2.2kW 50hZ compressor is approximately 66 Amps

The compressor must be free of residue pressure, the gauge must read 0 bar before start up otherwise AMPS could be more”


“The answer is 83 Amps.

At the start, the electric motors need a variable amount of Ampere from 3 to over 5 times those written on the plate.

It depends on the type of engine and where you get the electrical power from.

I'll give you an example:

3kw 16Ampere in the house and the compressor is able to start and work.

However, if you have to use a power generator, it must be at least 8KVA otherwise it won't start.”

In top of this compressor,

electric induction hob, 12V fridge 100L, lights, laptop 4h/day, phone charging, standard 12v lights.



I don’t know which type of investor /MPPT and batteries he should use ? Plus other useful bits ...

Thanks for advising me. XX


Cecile

@Vanpuravida

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1 Answer
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Mike Dorsett answered ·

This is a similar problem to installing this compressor on a Yacht, which I did back in 2000. Then I used a 3 phase motor, and a three phase generator of 4kW, but still had problems starting the compressor. I ended up installing a dump valve on the output of stage1 and direct drive the compressor off the diesel engine. Now, with EV development having made some great bounds in the last 20 years, I've rebuilt the compressor to use a 3kW 48Vdc Brushless DC Motor, with an appropriate controller.

IF you want to proceed with the 240V I think you will end up with a 15kW inverter to get the compressor to start (most of the time). I don't think Running this from an AC inverter will be economical as you will end up with an oversize inverter for the rest of the loads.

The DC Motor option was quite cheap - $500 USD+shipping.

Energy: about 70A for 1/2 hour @ 48V = 1680kWh per fill. Battery MINIMUM must be able to safely deliver 80 - 100A continuous for 1/2 hour, so min 4kWh or 85Ah@ 48V (lithium - double or 3 times for lead).

If you get say 3kWh/kW per day irradiation, you would need a 300W panel just for this, so 370W of panel would be a minimum. Problem would then be charging 48V from a single panel with Voc ~ 40 - 45V. 2 smaller modules in series would be easier - say 2 x 200W with an MPPT 100/50.

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lahma avatar image lahma commented ·

Mike - I came across this reply a bit late :), but I'm very curious to hear more about the 48v DC motor swap on your compressor. Which compressor and which 48v motor+controller? Any hiccups with the setup? Able to run the compressor at full speed?

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